Anhedonia in postpartum rats

Abstract

Postpartum depression (PPD) is a debilitating illness, yet little is known about its causes. The purpose of this study was to examine a major symptom of depression during the postpartum period, anhedonia, by comparing sucrose preference in female rats that had undergone actual pregnancy or hormone-simulated pregnancy (HSP) to their respective controls. Whereas HSP rats showed significantly less preference than vehicle control rats for 1% sucrose solution during the first three weeks of the "postpartum" period, previously pregnant females showed only slightly depressed sucrose preference for the first 1-2 days postpartum, compared to non-pregnant controls. Habituation to 1% sucrose during the pregnancy period, which increased preference upon later testing in previously pregnant rats tested on postpartum day 2, did not significantly increase preference in HSP rats, suggesting that depressed preference in the latter group was not due to neophobia. Pre-treatment with desipramine did not prevent suppressed sucrose preference in HSP rats, and preference was even further suppressed following chronic sertraline treatment. These results suggest that estradiol withdrawal following HSP may cause anhedonia during the early "postpartum" period. In contrast, females that have undergone actual pregnancy are less likely to show this effect, suggesting that postpartum hormonal changes other than the dramatic decline in estradiol may buffer its negative mood effects.

Figure 1

Top panels: Percent preference (mean ± 1 S.E.M) for a 1% sucrose solution during the postpartum period, in HSP vs. vehicle control rats (left; N=5–11 rats/treatment group/time point), and in previously pregnant vs. non-pregnant control rats (right; N=6–14 rats/group/time point). The dotted line at 50% preference denotes equal consumption of sucrose and water (i.e. no preference for sucrose); data points above this line reflect a preference for sucrose solution over water. Bottom panels: Body-weight adjusted uterine weight in HSP vs. vehicle control rats (left; N=4–10 rats/group/time point), and in previously pregnant vs. non-pregnant control rats (right; N=6–7 rats/group/time point). *Significantly greater than control group, p≤0.05.

Figure 2

Percent preference (mean ± 1 S.E.M.) for 0.5%, 1% or 2% sucrose solutions on postpartum day 2, in HSP vs. vehicle control rats (left panel; N=8–12 rats/treatment group/[sucrose]), and in previously pregnant vs. non-pregnant control rats (right panel; N=7–10 rats/treatment group/[sucrose]). Other details as in Fig. 1.

Figure 3

Percent preference (mean + 1 S.E.M) for a 1% sucrose solution on postpartum day 2 in rats previously exposed to 1% sucrose (Habituation) vs. those not pre-exposed to sucrose (No Habituation). Left panel: HSP vs. vehicle control rats; N=11–12 rats/treatment group/habituation condition. Right panel: Previously pregnant vs. non-pregnant control rats; N=6–9 rats/treatment group/habituation condition. *Significantly different than non-habituated, vehicle control rats, P< 0.05. Other details as in Fig. 1.

Figure 4

Effect of sub-chronic or chronic pretreatment with antidepressant medications on preference for a 1% sucrose solution (mean + 1 S.E.M) in HSP rats on postpartum day 2. Rats were injected sub-chronically (3 injections over 1 day pre-test) or chronically (once-daily for 16 days) with vehicle, sertraline (10 mg/kg) or desipramine (10 mg/kg); N=4–8 rats/drug/regimen. *Significantly different than sub-chronic, vehicle control rats, P< 0.05. Other details as in Fig. 1.